A known magnetic disk drive typically includes a breathing hole drilled in an outer wall surface thereof, the hole providing communication between an outside and an inside of the drive. Atmosphere flows in and out of the drive through this breathing hole. Differential pressure between the inside and the outside of the drive produced during starting to rotate a magnetic disk or the like is thereby eliminated, so that the drive can be kept in a fully operational condition. (See, for example, Japanese Laid-Open Patent No. Sho 62-73484)
The magnetic disk drive has conventionally and commonly been used in a personal computer or the like that is fixedly installed indoors. This common application has precluded circumstances, in which water or other form of liquid enters the magnetic disk drive. Because of a new application of the magnetic disk drive arising lately in the field of CE (MP3 (MPEG Audio layer-3) players, cellular phones, mobile computers, and the like), however, there is greater likelihood that water or other form of liquid will enter the disk drive as a result of submersion under water, rainwater, and the like. The magnetic disk drive is a type of precision equipment and entry of water or other form of liquid in the magnetic disk drive is not desirable.